1. Field of the Invention
This invention relates to the stabilization of isothiazolones with various metal salts.
2. Description of the Prior Art
The use of 3-isothiazolones to control microbial growth in a variety of industrial environments (metal working fluids, cooling tower water, emulsions, plastic film, and the like) has been enhanced by the addition of stabilizers to maintain antimicrobial activity for longer periods of time; typical stabilizer systems include metal nitrates and the like.
U.S. Pat. Nos. 3,870,795 and 4,067,878 teach the stabilization of isothiazolones against chemical decomposition by addition of a metal nitrite or metal nitrate salts, but teach that other common metal salts, including carbonates, sulfates, chlorates, perchlorates, and chlorides are not as effective as nitrates or nitrites in stabilizing solutions of isothiazolones, such solutions usually being in water or in an hydroxylic solvent and immiscible with solvent-soluble isothiazolones. Salts or organic carboxylic acids of more than six carbon atoms with copper are not taught or considered in these patents.
U.S. Pat. Nos. 4,150,026 and 4,241,214 teach metal salt complexes of isothiazolones useful because of their enhanced thermal stability, while retaining biological activity. The metal salts listed do not include copper or zinc salts of organic carboxylic acids of six or more carbon atoms, or complexes of copper with organic-soluble reagents or polymers.
U.S. Pat. No. 4,608,183 teaches synergistic biocidal mixtures of isothiazolones and a metal complex with polyfunctional ligand, where the metal complex itself may be a biocide. Illustrated specifically is the water-soluble monocopper sodium citrate. It is known to use certain organic stabilizers for isothiazolones, generally for use situations where metal salts may create problems, such as corrosion, coagulation of latices, insolubility in non-aqueous media, interaction with the substrate to be stabilized, and the like.
Formaldehyde or formaldehyde-releasing chemicals are known stabilizers (see U.S. Pat. Nos. 4,165,318 and 4,129,448).
In certain applications, however, it is desirable to avoid addition of organic stabilizers by virtue of their volatility, decomposition under high heat, higher cost, difficulty in handling, potential toxicity, and the like. Formaldehyde is a suspected carcinogen, and it is desirable to reduce the use of formaldehyde or formaldehyde releasing chemicals in applications where contact with human skin or lungs may occur.
Grove, U.S. Pat. No. 4,783,221 teaches blends of the isothiazolones of the present invention with at least one metal salt of an organic carboxylic acid of at least six carbon atoms, wherein the metal is a transition metal, zinc, mercury, antimony, or lead, and also with a solvent diluent. The patent is directed to wood preservative compositions and does not teach or suggest use in metalworking fluids, cooling tower water, and the like. Further, Grove does not teach of enhanced stability of these compositions.